In the past, tin (Sn)-lead (Pb)-type solder alloys containing large quantities of lead have been heavily used as solder for electrical connections inside electronic components, or for connecting electronic components to a circuit board.
Recently, the harmful effects of lead have been viewed as a problem, and legally restricting its use has been considered. For these reasons, development is being speeded up of a solder alloy with an extremely low lead content, or a lead-free solder alloy containing absolutely no lead ingredients as a substitute for Sn—Pb-type solder alloy.
Japanese Patent No. 3036636 and U.S. Pat. No. 4,758,407 can be cited as examples of lead-free solder alloys.
Patent No. 3036636 relates to a lead-free solder alloy for attaching electronic components to a circuit board of an electronic device, with nickel (Ni) substituted for a portion of the copper ingredient of the tine (Sn)-copper (Cu) alloy, aimed at enhancing the mechanical strength of the aforementioned attached portions by bringing the ingredient ratios to 0.05 to 2.0 wt % of Cu and 0.001 to 2.0 wt % of Ni, with the remainder consisting of Sn.
As previously described, this solder alloy is used in reflow soldering for attaching electronic components to the conducting portion of a circuit board, and the service temperature (temperature at the time of soldering) thereof is approximately 230° C.
U.S. Pat. No. 4,758,407 also proposes the use of copper pipe and brass pipe in plumbing, to inhibit the release of lead and cadmium into drinking water from lead piping used in plumbing, and this patent relates to a solder alloy for welding these copper pipes and brass pipes with the connecting joints for extending them.
This solder alloy also has tin (Sn), or tin (Sn) and antimony (Sb) as its main ingredients, and never contains lead (Pb) or cadmium (Cd).
In this case, the solder alloy that primarily comprises tin is composed of 92.5 to 96.9 wt % Sn, 3.0 to 5.0 wt % 0.1 to 2.0 wt % Ni, and 0.0 to 5.0 wt % Ag.
Also, the solder alloy that primarily comprises tin and antimony is composed of 87.0 to 92.9 wt % Sn, 4.0 to 6.0 wt % Sb, 3.0 to 5.0 wt % Cu, 0.0 to 2.0 wt % Ni, and 0.0 to 5.0 wt % Ag.
The melting temperature of this solder alloy is from about 240° C. to about 330° C., but because this solder alloy is used, for example, to weld copper pipes, brass pipes, and joints thereof in the water supply lines of household water heaters, it is better for the solder alloy to have a low melting temperature when considering workability and the like during welding.
In addition, electronic components include high-frequency coils and transformers (hereafter referred to as coil components) formed by coiling wire-shaped or narrow band-shaped electric conductors (hereafter referred to as winding wire). Insulation-coated electric wire obtained by applying enamel, urethane, or the like to a copper core wire to form an insulating film is used as the coiled wire material for these coil components.
The abovementioned coil components are soldered in order to electrically connect the outgoing end portion of the winding wire wrapped around a bobbin or the like to a terminal pin or other electrode portion provided in the bobbin. To electrically connect the terminal pin or the like with the end portion of the winding wire, the insulating coating material on the aforementioned end portion of the winding wire must be removed. In general, methods for removing the insulating coating material on the aforementioned insulation-coated electric wire include mechanical scraping methods, chemical dissolution methods, and methods of decomposition or dissolution by high-temperature heating.
Methods that employ high-temperature heating are widely used in conventional practice.
The coil components are manufactured by wrapping the end portion of the winding wire onto the terminal pin and dipping the wrapped part in a bath of liquid solder heated to high temperature, and soldering is performed at the same time as the insulating coating material of the winding wire is dissolved and removed by the heat of the solder liquid.
During soldering of the aforementioned wrapped portion of the end portion with the terminal pin, a phenomenon known as “copper erosion” occurs when a lead-free solder alloy that contains no copper ingredient is used. In this phenomenon, the copper base metal of the insulation-coated electric wire (winding wire) dissolves in the solder liquid and becomes thin while the aforementioned wrapped portion is in contact with the molten solder (solder liquid). This “copper erosion” phenomenon is a major contributing factor to the occurrence of accidental wire breakage in electronic components such as the abovementioned coil components.
By this effect, the quantity of copper that melts into the aforementioned solder liquid increases, and the speed of copper melting increases, in direct proportion to the melting temperature of the solder liquid. Consequently, the abovementioned accidental wire breakage becomes more likely with a reduction in the wire diameter of the winding wire.
On the other hand, means for adding a trace quantity of copper to the aforementioned lead-free solder alloy are generally known for inhibiting the “copper erosion” phenomenon, but if the copper content is too large, the viscosity of the molten solder (solder liquid) becomes high, and an excessive amount of solder is applied to the soldered parts between neighboring terminals and the like during soldering, leading to bridging phenomena wherein these terminals electrically short, unevenness in plating thickness (quantity of applied solder), deterioration of wetting characteristics, and other defects.
Bridging effects become more likely as the electronic components become more miniaturized, and the distances (pitch) between neighboring terminals become more narrow.
However, if the melting temperature of the molten solder is lowered to reduce the aforementioned “copper erosion” in the lead-free solder alloy, the enamel, urethane, or other insulating coating material of the end portion of the winding wire does not completely dissolve, the residue of the aforementioned coating material is deposited on the aforementioned wrapped part, and soldering is left incomplete, contributing to conduction defects. The aforementioned residue is also a contributing factor to the abovementioned bridging.
The inventors discovered that “copper erosion” could be prevented, and the post-soldering mechanical strength of the lead-free solder alloy increased, by first adding nickel (Ni) in a lead-free solder alloy obtained by adding appropriate quantities of copper (Cu) and nickel (Ni) to tin (Sn).
However, it is preferable to increase the copper content of this lead-free solder alloy as well to adequately prevent the “copper erosion” phenomenon, but as the copper content increases, the viscosity of the solder alloy when melted becomes high, and dispersion of the solder liquid deteriorates. Consequently, bridging effects are likely to occur in the soldering of electronic components such as miniature coil components with narrow distances (pitch) between neighboring terminals such as those described above.
Therefore, an object of the present invention is to provide a lead-free solder alloy that adequately maintains characteristics for suppressing “copper erosion” in a lead-free solder alloy of the tin-copper-nickel type, and in which the viscosity of the molten solder (solder liquid) is lowered.